A display device having a flexible image display portion, such as a film liquid crystal display and a flexible organic EL display, has attracted attention from the standpoint of convenience and portability.
Such a display device uses a flexible display substrate as a main body component. The flexible display substrate has an image display region for displaying images and a mounting region for mounting an electronic component (for example, a driver IC) that processes a video signal of the image display device on a flexible substrate, such as a plastic film having flexibility and high transparency.
When the electronic component is mounted, it is common that a thermosetting anisotropic conductive film is arranged on the mounting region, the electronic component is arranged on the anisotropic conductive film, and then, the electronic component is fixed using the anisotropic conductive film by heating and pressing. It is noted that in order to further improve the flexibility of the flexible display substrate, reducing the thickness or rigidity of the plastic film serving as a substrate causes deformation or distortion of the substrate during the heating and pressing as described above, and likely leads to degradation of display images.
Wiring boards or flexible printed wiring boards, although different from that of the flexible display substrate described above, share a common feature with the flexible display substrate in that they both use a flexible substrate. In the technical field of flexible printed wiring boards, there is a technique of adhering a reinforcing plate (a backing plate) to the back surface of an external terminal region formed at the end part of the wiring board, and thus, providing a support against heat and stress applied to the end part by using the reinforcing plate on the back surface. This technique allows avoiding distortion or deformation occurring during the penetration into other components and the mounting of the electronic component on the wiring board.
Specific examples of the above-discussed reinforcing plate include a thermosetting-type reinforcing plate, such as a thermosetting sheet like those described in Patent Literatures 1 to 3, and an adhesion sheet like those described in Patent Literatures 4 and 5.